// vim: shiftwidth=4 tabstop=4 noexpandtab

package main

import (
	"bytes"
	"encoding/json"
	"flag"
	"fmt"
	"io/ioutil"
	"log"
	"net/http"
	"net/netip"
	"text/template"
)

type RuntimeConfig struct {
	Devices DevicesConfig
	Web     WebConfig
}

type DevicesConfig struct {
	Hs100 []Hs100Conf
}

type WebConfig struct {
	Listen netip.AddrPort
}

// main() contains the control flow of this program.
func main() {
	configPath := parseFlags()
	config := parseConfig(configPath)
	http.HandleFunc("/", index(config.Devices))
	http.HandleFunc("/api", api())
	http.HandleFunc("/webiot.css", css())
	fmt.Printf("Serving at http://%s\n", config.Web.Listen)
	log.Fatal(http.ListenAndServe(config.Web.Listen.String(), nil))
}

// parseFlags() handles command line interface (CLI) flags.
func parseFlags() string {

	var r string // return value

	flag.StringVar(&r, "c", "/etc/webiot/config.json",
		"path to configuration file")
	flag.Parse()

	return r
}

// parseConfig() parses and validates the runtime configuration file and
// returns it as Go datastructure.
func parseConfig(path string) RuntimeConfig {

	// read config file and ensure proper JSON formatting
	data := mustRead(path)
	if !json.Valid(data) {
		log.Fatalf("%s contains invalid JSON!", path)
	}

	// read to RuntimeConfig struct and handle errors
	config := RuntimeConfig{}
	err := json.Unmarshal(data, &config)
	if err != nil {
		log.Fatalf("Could not parse configuration file:\n%s\n", err)
	}

	return config
}

// index() returns a HTTP handler for the index page.
func index(config DevicesConfig) func(http.ResponseWriter, *http.Request) {

	// prepare HTML
	html := mustRender("index.html.tmpl", config)

	return func(w http.ResponseWriter, r *http.Request) {
		fmt.Fprint(w, html)
	}
}

func css() func(http.ResponseWriter, *http.Request) {

	// read CSS file
	css := string(mustRead("./libweb/libweb.css"))

	return func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Content-Type", "text/css; charset=utf-8")
		fmt.Fprint(w, css)
	}
}

// mustRead() reads a file and panics if this is not possible.
func mustRead(path string) []byte {
	data, err := ioutil.ReadFile(path)
	if err != nil {
		log.Fatalf("Could not read '%s'!", path)
	}
	return data
}

// mustRender() renders a template file with the given data and panics if this
// is not possible.
func mustRender(filepath string, data interface{}) string {

	file := mustRead(filepath)
	tmpl, err := template.New(filepath).Parse(string(file))
	var buffer bytes.Buffer
	err = tmpl.Execute(&buffer, data)
	if err != nil {
		fmt.Println(err)
		log.Fatalf("Could not execute template for %s!", filepath)
	}

	return buffer.String()
}

// api() returns the HTTP handler for the API endpoint.
func api() func(http.ResponseWriter, *http.Request) {
	return func(w http.ResponseWriter, r *http.Request) {

		// TODO assert correct HTTP method

		// read parameters and handle errors
		errHost, host := assertSingleParam(r, "host")
		errState, state := assertSingleParam(r, "state")
		if (errHost != nil) || (errState != nil) {
			http.Error(w,
				"Provide exactly one host and one state parameter!", 400)
			return
		}

		// set WiFi plug
		err := set(host, state)
		if err != nil {
			http.Error(w, "Could not set WiFi plug.", 500)
		} else {
			fmt.Fprint(w, "ok")
		}
	}
}

// assertSingleParam() returns the value of given URL key and panics if there
// is not exactly one match for this key.
func assertSingleParam(r *http.Request, key string) (error, string) {

	values := r.URL.Query()[key]
	if len(values) != 1 {
		return fmt.Errorf("Provide exactly one '%s' parameter!", key), ""
	}
	return nil, values[0]

}